193nm laser and inspection system

Abstract

An improved solid-state laser for generating sub-200 nm light is described. This laser uses a fundamental wavelength between about 1030 nm and 1065 nm to generate the sub-200 nm light. The final frequency conversion stage of the laser creates the sub-200 nm light by mixing a wavelength of approximately 1109 nm with a wavelength of approximately 234 nm. By proper selection of non-linear media, such mixing can be achieved by nearly non-critical phase matching. This mixing results in high conversion efficiency, good stability, and high reliability.

The invention claimed is: 
     
       1. A laser for generating sub-200 nm wavelength light, the laser comprising:
 a fundamental laser configured to generate a fundamental wavelength between about 1030 nm and 1065 nm; 
 a plurality of harmonic generators configured to convert the fundamental wavelength into first light having a wavelength of approximately 1109 nm and second light having a wavelength of approximately 234 nm; and 
 a frequency mixing stage configured to combine said first light at said wavelength of approximately 1109 nm with said second light at said wavelength of approximately 234 nm to generate said sub-200 nm wavelength light at a wavelength between 190 nm and 200 nm. 
 
     
     
       2. The laser of  claim 1 , wherein the plurality of harmonic generators and the frequency mixing stage are configured such that said sub-200 nm wavelength light has a wavelength of substantially 193.4 nm. 
     
     
       3. The laser of  claim 1 , wherein the plurality of harmonic generators comprises a first generator configured to generate said first light at said wavelength of approximately 1109 nm by Raman shifting the fundamental wavelength. 
     
     
       4. The laser of  claim 3 , wherein the first generator comprises a Raman amplifier including one of an undoped fused-silica fiber and a Germania-doped fused silica fiber. 
     
     
       5. The laser of  claim 1 , wherein the plurality of harmonic generators comprises a second generator including:
 one of an optical parametric oscillator and an optical parametric amplifier that is pumped by the fundamental wavelength and configured to generate double-wavelength light having a wavelength of approximately 2218 nm; and 
 a second harmonic generator configured to receive the double-wavelength light and to generate said first light having said wavelength of approximately 1109 nm. 
 
     
     
       6. The laser of  claim 1 , wherein said frequency mixing stage includes a CLBO (cesium lithium borate) crystal. 
     
     
       7. The laser of  claim 1 , wherein said frequency mixing stage includes a non-linear optical crystal that has been annealed in a hydrogen environment. 
     
     
       8. The laser of  claim 1 , wherein the plurality of harmonic generators comprises a third generator including:
 a third harmonic generator configured to generate a third harmonic of the fundamental wavelength; and 
 a first frequency mixer configured to generate said second light at said wavelength of approximately 234 nm by mixing the third harmonic of the fundamental wavelength with light at a wavelength of approximately 689 nm. 
 
     
     
       9. The laser of  claim 1 , wherein the plurality of harmonic generators comprises a fourth generator including:
 a fourth harmonic generator configured to generate a fourth harmonic of the fundamental wavelength; and 
 a second frequency mixer configured to generate said second light at said wavelength of approximately 234 nm by mixing the fourth harmonic of the fundamental with light at a wavelength of approximately 1954 nm. 
 
     
     
       10. The laser of  claim 1 , wherein the plurality of harmonic generators comprises:
 a fifth generator configured to generate third light at a wavelength of approximately 1171 nm; and 
 a fifth harmonic generator configured to generate said second light at said wavelength of approximately 234 nm from said third light at said wavelength of approximately 1171 nm. 
 
     
     
       11. The laser of  claim 10 , wherein the fifth generator comprises a fiber optical parametric oscillator configured to receive a pump laser light having a pump wavelength determined by one of the first light and said fundamental frequency, said fifth generator including a Raman amplifier configured to generate one of a first-order Raman shift and a second-order Raman shift from the pump wavelength. 
     
     
       12. The laser of  claim 11 , wherein the fifth harmonic generator comprises:
 a second harmonic generator configured to receive said third light at said wavelength of approximately 1171 nm and to generate a second harmonic; 
 a third harmonic generator configured to receive said second harmonic and to generate a third harmonic; and 
 a fifth harmonic generator configured to receive said third harmonic and to generate said second light at said wavelength of approximately 234 nm. 
 
     
     
       13. The laser of  claim 1 , wherein plurality of harmonic generators are configured such that the second light at said wavelength of approximately 234 nm is at a wavelength of substantially 234.2 nm. 
     
     
       14. The laser of  claim 1 , wherein the fundamental laser comprises one of an ytterbium-doped fiber laser, a neodymium-doped yttrium-aluminum-garnate laser, a neodymium-doped yttrium-orthovanadate laser, and a neodymium-doped yttrium-lithium-fluoride laser. 
     
     
       15. A method of generating sub-200 nm wavelength laser light, the method comprising:
 generating a fundamental wavelength between about 1030 nm and 1065 nm; 
 using the fundamental wavelength to generate first light having a wavelength of approximately 1109 nm; 
 using the fundamental wavelength to generate second light having a wavelength of approximately 234 nm; 
 combining the first light having the wavelength of approximately 1109 nm and the second light having the wavelength of approximately 234 nm to generate said sub-200 nm wavelength laser light having a wavelength between 190 nm and 200 nm. 
 
     
     
       16. The method of  claim 15 , wherein generating the first light having the wavelength of approximately 1109 nm comprises Raman shifting the fundamental wavelength. 
     
     
       17. The method of  claim 16 , wherein the method further comprises amplifying the first light having the wavelength of approximately 1109 nm using one of a fiber-optic amplifier, a doped-fiber-optic amplifier, a Germania-doped silica fiber Raman amplifier, and an undoped silica fiber Raman amplifier. 
     
     
       18. The method of  claim 15 , wherein generating the first light having the wavelength of approximately 1109 nm comprises frequency doubling an output of one of an optical parametric oscillator and optical parametric amplifier that is pumped by the fundamental wavelength. 
     
     
       19. The method of  claim 15 , wherein combining the first light having the wavelength of approximately 1109 nm and the second light having the wavelength of approximately 234 nm comprises mixing said first light and said second light in a CLBO (cesium lithium borate) crystal. 
     
     
       20. The method of  claim 15 , wherein combining the first light having the wavelength of approximately 1109 nm and the second light having the wavelength of approximately 234 nm comprises mixing said first light and said second light in a non-linear optical crystal that has been annealed in a hydrogen environment. 
     
     
       21. The method of  claim 15 , wherein generating the second light having the wavelength of approximately 234 nm comprises mixing a third harmonic of the fundamental wavelength with light at a wavelength of approximately 689 nm. 
     
     
       22. The method of  claim 15 , wherein generating the second light having the wavelength of approximately 234 nm comprises mixing a fourth harmonic of the fundamental wavelength with light at a wavelength of approximately 1954 nm. 
     
     
       23. The method of  claim 15 , wherein generating the second light having the wavelength of approximately 234 nm comprises creating a fifth harmonic of third light having a wavelength of approximately 1171 nm. 
     
     
       24. The method of  claim 15 , wherein generating the fundamental wavelength comprises using one of an ytterbium-doped fiber laser, a neodymium-doped yttrium-aluminum-garnate laser, a neodymium-doped yttrium-orthovanadate laser, and a neodymium-doped yttrium-lithium-fluoride laser.